Modern vehicles are increasingly equipped with so-called driver assistance systems that support the driver of a motor vehicle, for example when driving the vehicle in moving traffic, and also for example when parking the vehicle along the side of a roadway.
In the processing carried out by a driver assistance system, it is desirable to distinguish between those objects that can be driven over safely by the motor vehicle (for example empty beverage containers lying on the ground) and those objects that must not be driven over by the vehicle (for example a parking car or a tree). Here, it is helpful to determine, in addition to the azimuthal angular position of a detected object, the elevation angle as well, i.e. the vertical position of the object.
German patent application DE 10 2010 064 348 A describes a radar sensor for motor vehicles. The configuration of the antennas here can be controlled in such a way that it has a directional characteristic that varies with time. By evaluating radar echoes, an elevation angle of detected objects can be determined.
One possibility for determining an elevation angle is to supplement a radar sensor system with an additional elevation antenna. This elevation antenna has a directional characteristic that differs, in the elevation direction, from the characteristic of the antennas of the main system. If the amplitudes of the received signals originating from a transmit pulse of the elevation antenna are compared with the amplitudes of those signals originating from a transmit pulse of the main antennas, from this comparison of the amplitudes it is possible to infer an elevation angle of an object. The taking into account of the amplitudes can be directed either to the analysis of the magnitude of the amplitudes, or alternatively can evaluate the complex amplitudes as to their magnitude and phase.
However, if more than one object is simultaneously located in the sector of a radar cell, then in this case it is no longer possible to make an unambiguous determination of the elevation angle from the comparison of the amplitudes of the received signals.
Therefore, there is a need for a radar system that, when more than one object is situated within a radar cell, is capable of reliably determining an elevation angle. In addition, there is also a need for a radar system that, when more than one object is situated within a radar segment, enables a reliable classification of the objects.